Lubricating oils include gear oils for industrial use, engine oils, lubricating oils for refrigerators, lubricating oils for fibers, lubricating oils for rolling, oils for electric insulation and the like oils.
As it has now been urged to operate industrial machinery under ever severe conditions, it has been demanded to produce gear oils for industrial use that are capable of maintaining lubricating property and cleaning property up to high temperature ranges. In a step of baking finish and a step of baking foods, in particular, higher performance is required in regard to lubricating property and cleaning property. For such applications, there have heretofore been used lubricating oils of the types of synthetic hydrocarbons, carboxylic esters and glycols.
However, the synthetic hydrocarbon oils and carboxylic ester oils are not still satisfactory in regard to lubricating property, form carbonates after heated for extended periods of time, and are not capable of playing the role of lubricating oils under high-temperature conditions. On the other hand, the glycol lubricating oils have a merit of forming carbonates in small amounts even after heated for extended periods of time but have insufficient lubricating property and strong hygroscopic property, leaving room for improvement in regard to lubricating property and hygroscopic property.
Accompanying the trend toward producing automotive engines of higher performance, furthermore, it has been urged to produce engine oils that maintain lubricating property, cleaning property and dispersing property at higher temperatures even after used for longer periods of time. If it is attempted to meet such demands by selecting additives, the additives are inevitably used in large amounts bringing about a harmful effect, i.e., sedimentation of a mayonnaise sludge. It has heretofore been attempted to use a mineral oil as a base oil together with the synthetic hydrocarbon oil or the carboxylic ester oil without, however, satisfactory results in regard to lubricating property, cleaning property and dispersing property when used at high temperatures for extended periods of time. Unlike the lubricating oils for the automotive engines, i.e., for the four-cycle engines, on the other hand, the lubricating oils for the two-cycle engines are burned being added to the gasoline and, hence, its cleaning property is most important. Castor oils and polybutenes have heretofore been used as lubricating oils for the two-cycle engines, but their lubricating property and cleaning property are not still satisfactory.
Gear oils for automobiles and, particularly, gear oils for ATF must have small coefficients of friction and must be aged little. Therefore, there have heretofore been used a friction-reducing agent and a friction-adjusting agent. However, gear oils for automobiles containing these additives still have a problem in that their coefficients of friction change greatly with the passage of time.
So far, lubricating oils of the types of carboxylic ester and glycol have been used for the fibers satisfying, however, neither lubricating property nor cleaning property.
A lubricating oil chiefly consisting of beef tallow has long been used for the rolling. This lubricating oil features excellent lubricating property and rolling efficiency but has very poor cleaning property, making it necessary to carry out the step of cleansing the beef tallow. Moreover, a lubricating oil of the type of carboxylic ester has been used for the rolling featuring very good cleaning property but low practicability because of its poor lubricating property.
In the refrigerators in which ozone layer non-depleting R-134a (CH.sub.2 F--CF.sub.3) has now been used as the coolant gas, mineral oils and alkylbenzene compounds that were used as lubricating oils are now no longer usable because they lack compatibility with the coolant gas. At present, a glycol ether lubricating oil has been developed for lubricating the refrigerators that use the above-mentioned coolant gas.
U.S. Pat. No. 4,755,316 discloses a composition for compression refrigerators, comprising a tetrafluoroethane and a polyoxyalkylene glycol having a molecular weight of 300 to 2,000 and a kinematic viscosity of about 25 to 150 cst at 37.degree. C.
However, the glycol ether lubricating oils have insufficient heat stability, strong hygroscopic property and cause rubber sealing members such as of NBR to shrink and hardened.
In modern refrigerators for car air conditioners, furthermore, there has been employed a through-vane type rotary compressor featuring both reduced size and increased efficiency. The lubricating oil for the through-vane type rotary compressor must have a large viscosity from the standpoint of sealing property and wear resistance. However, compounds having a glycol ether structure are not utilizable since they exhibit poor compatibility with respect to the ozone layer non-depleting R-134a when their molecular weights are increased to exhibit increased viscosities.
In recent years, furthermore, poly ester and carboxylic ester lubricating oils called hindered ester have been developed for lubricating the refrigerators that use the ozone layer non-depleting hydrogenated fluorocarbons (HFC) as the coolant. However, these lubricating oils form carboxylic acid upon the hydrolysis or the thermal decomposition resulting in the occurrence of corrosion and wear of metals or copper-plating phenomenon in the refrigerators due to the carboxylic acid. Therefore, these lubricating oils bring about a problem concerning the durability of the refrigerators.
In the electric refrigerators and room air conditioners, furthermore, the electric wirings are immersed in the lubricating oil. Therefore, leakage of current and short-circuiting must be avoided. From this point of view, the lubricating oil for the electric refrigerators and room air conditioners must have excellent electrically insulating property in addition to lubricating property and compatibility with the hydrogenated fluorocarbons. However, the carboxylic ester lubricating oils have poor electrically insulating property and are not suited for the electric refrigerators and room air conditioners.
It has therefore been desired to provide a lubricating oil having excellent lubricating property and electrically insulating property yet exhibiting excellent compatibility with ozone layer non-depleting hydrogenated fluorocarbons such as R-134a.